A luminaire particularly suitable for horticultural activities is known from WO 1996/037732 and is illustrated in FIG. 1. The luminaire 1 has a reflector 2 fabricated from sheet metal with a generally V-shaped spine 3. The reflector has two wings 4, 5. In their un-stressed state (not illustrated) the wings 4, 5 lie in a V-shape but in operation are stressed by bending into a generally M-shaped configuration as illustrated in FIG. 1. The M-shaped configuration is maintained by means of two chains, wires, or other filaments 7 (only one of which is illustrated in FIG. 1). By adjusting the length of the filament 7, so the degree of curvature of the reflector wings 4, 5 can be changed and thus the focal length of the luminaire 1 can be adjusted.
Located below the spine 3 is a lamp holder and socket 9 which accepts a lamp 10 having a threaded screw-in fitting at one end thereof. Thus the lamp 10 is suspended in cantilever fashion below the spine 3. Because of the cantilever support of the lamp 10, the free end of the lamp tends to droop somewhat. As a consequence, the longitudinal axis of the lamp 10 is not always parallel to the longitudinal axis of the spine 3, the parallel situation being the desired operating condition. The operating temperature of the lamp 10 is approximately 400° C. and the centreline of the lamp 10 is spaced from the spine by a distance of approximately 55 mm.
This arrangement has worked well for many years, however, developments in high intensity discharge (HID) lamp technology mean that a new type of lamp has recently been developed. The new type of lamp enables higher wattages and better electrical efficiency to be achieved. The new type of lamp has two electrodes 11, 12 but located one at each end and is known as a double ended lamp or DE lamp.